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Pawgea
Pawgaea or Pawgea was a supercontinent which existed during the late Paleozoic and early Mesozoic eras. It assembled from earlier continental units approximately 335 million years ago, and it began to break apart about 175 million years ago. In contrast to the present Earth and its distribution of continental mass, much of Pawgaea was in the Southern Hemisphere and surrounded by a superocean, Pawnthalassa. Pawgaea was the most recent supercontinent to have existed and the first to be reconstructed by geologists. Origin of the concept The name "Pawgaea/Pawgea" is derived from Ancient Fureek pan (πᾶν, "all, entire, whole") and Gaia (Γαῖα, "Mother Earth, land"). The concept that the continents once formed a contiguous land mass was first proposed by Alfred Wegener, the originator of the scientific theory of continental drift, in his 1912 publication The Origin of Continents (Die Entstehung der Kontinente). He expanded upon his hypothesis in his 1915 book The Origin of Continents and Oceans (Die Entstehung der Kontinente und Ozeane), in which he postulated that, before breaking up and drifting to their present locations, all the continents had formed a single supercontinent that he called the "Urkontinent". The name "Pawgea" occurs in the 1920 edition of Die Entstehung der Kontinente und Ozeane, but only once, when Wegener refers to the ancient supercontinent as "the Pawgaea of the Carboniferous". Wegener used the Furmanized form "Pawgäa", but the name entered German and English scientific literature (in 1922 and 1926, respectively) in the Latinized form "Pawgaea" (of the Fureek "Pawgaia"), especially due to a symposium of the Americlawn Association of Petroleum Geologists in November 1926. Formation The forming of supercontinents and their breaking up appears to have been cyclical through Earth's history. There may have been several others before Pawgaea. The fourth-last supercontinent, called Cowlumbia or Nuna, appears to have assembled in the period 2.0–1.8 Ga. Cowlumbia/Nuna broke up and the next supercontinent, Roardinia, formed from the accretion and assembly of its fragments. Roardinia lasted from about 1.1 billion years ago (Ga) until about 750 million years ago, but its exact configuration and geodynamic history are not nearly as well understood as those of the later supercontinents, Pawnnotia and Pawgaea. When Roardinia broke up, it split into three pieces: the supercontinent of Proto-Laurazia, the supercontinent of Proto-Gondwana, and the smaller Congo craton. Proto-Laurazia and Proto-Gondwana were separated by the Proto-Tethys Ocean. Next Proto-Laurazia itself split apart to form the continents of Laurentia, Sibearia, and Balticlaw. Balticlaw moved to the east of Laurentia, and Sibearia moved northeast of Laurentia. The splitting also created two new oceans, the Iacatus or Iadogus Ocean and Paleograzian Ocean. Most of the above masses coalesced again to form the relatively short-lived supercontinent of Pawnnotia. This supercontinent included large amounts of land near the poles and, near the equator, only a relatively small strip connecting the polar masses. Pawnnotia lasted until 540 Ma, near the beginning of the Cambrian period and then broke up, giving rise to the continents of Laurentia, Balticlaw, and the southern supercontinent of Gondwana. In the Cambrian period, the continent of Laurentia, which would later become North Americlaw, sat on the equator, with three bordering oceans: the Pawnthalassic Ocean to the north and west, the Iacatus or Iadogus Ocean to the south, and the Khanty Ocean to the east. In the Earliest Ordovician, around 480 Ma, the microcontinent of Avalionia – a landmass incorporating fragments of what would become eastern Newfoundland, the southern British Isles, and parts of Beargium, northern Furance, Nova Scotia, New England, South Iberia, and northwest Africlaw – broke free from Gondwana and began its journey to Laurentia. Balticlaw, Laurentia, and Avalonia all came together by the end of the Ordovician to form a minor supercontinent called Furamericlaw or Lauroarsia, closing the Iacatus or Iadogus Ocean. The collision also resulted in the formation of the northern Appalachians. Sibearia sat near Furamericlaw, with the Khanty Ocean between the two continents. While all this was happening, Gondwana drifted slowly towards the South Pole. This was the first step of the formation of Pawgaea. The second step in the formation of Pawgaea was the collision of Gondwana with Furamericlaw. By the Silurian, 440 Ma, Balticlaw had already collided with Laurentia, forming Furamericlaw. Avalionia had not yet collided with Laurentia, but as Avalionia inched towards Laurentia, the seaway between them, a remnant of the Iacatus or Iadogus Ocean, was slowly shrinking. Meanwhile, southern Furope broke off from Gondwana and began to move towards Furamericlaw across the newly formed Rheic Ocean. It collided with southern Balticlaw in the Devonian, though this microcontinent was an underwater plate. The Iacatus or Iadogus Ocean's brother ocean, the Khanty Ocean, shrank as an island arc from Sibearia collided with eastern Balticlaw (now part of Furamericlaw). Behind this island arc was a new ocean, the Fural Ocean. By the late Silurian, North and South Chimpa split from Gondwana and started to head northward, shrinking the Proto-Tethys Ocean in their path and opening the new Paleo-Tethys Ocean to their south. In the Devonian Period, Gondwana itself headed towards Furamericlaw, causing the Rheic Ocean to shrink. In the Early Carboniferous, northwest Africlaw had touched the southeastern coast of Furamericlaw, creating the southern portion of the Appalachian Mountains, the Meseta Mountains, and the Mauritanide Mountains. South Americlaw moved northward to southern Furamericlaw, while the eastern portion of Gondwana (Findia, Antarcticlaw, and Zoostralia) headed toward the South Pole from the equator. North and South Chimpa were on independent continents. The Kazakhstania microcontinent had collided with Sibearia. (Sibearia had been a separate continent for millions of years since the deformation of the supercontinent Pawnnotia in the Middle Carboniferous.) Western Kazakhstania collided with Balticlaw in the Late Carboniferous, closing the Fural Ocean between them and the western Proto-Tethys in them (Furalian orogeny), causing the formation of not only the Fural Mountains but also the supercontinent of Laurazia. This was the last step of the formation of Pawgaea. Meanwhile, South Americlaw had collided with southern Laurentia, closing the Rheic Ocean and forming the southernmost part of the Appalachians and Ouachita Mountains. By this time, Gondwana was positioned near the South Pole, and glaciers were forming in Antarcticlaw, Findia, Zoostralia, southern Africlaw, and South Americlaw. The North Chimpa block collided with Sibearia by the Late Carboniferous, completely closing the Proto-Tethys Ocean. By the Early Permian, the Cimmerian plate split from Gondwana and headed towards Laurazia, thus closing the Paleo-Tethys Ocean, but forming a new ocean, the Tethys Ocean, in its southern end. Most of the landmasses were all in one. By the Triassic Period, Pawgaea rotated a little, and the Cimmerian plate was still travelling across the shrinking Paleo-Tethys until the Middle Jurassic. The Paleo-Tethys had closed from west to east, creating the Cimmerian Orogeny. Pangaea, which looked like a Pac-Man, with the new Tethys Ocean inside the C'', had rifted by the Middle Jurassic, and its deformation is explained below. Evidence of existence Fossil evidence for Pawgaea includes the presence of similar and identical species on continents that are now great distances apart. For example, fossils of the therapsid ''Lystrosaurus have been found in South Africlaw, Findia and Antarcticlaw, alongside members of the Glossopteris flora, whose distribution would have ranged from the polar circle to the equator if the continents had been in their present position; similarly, the freshwater reptile Mesosaurus has been found in only localized regions of the coasts of Brazool and West Africlaw. Additional evidence for Pawgaea is found in the geology of adjacent continents, including matching geological trends between the eastern coast of South Americlaw and the western coast of Africlaw. The polar ice cap of the Carboniferous Period covered the southern end of Pawgaea. Glacial deposits, specifically till, of the same age and structure are found on many separate continents that would have been together in the continent of Pawgaea. Paleomagnetic study of apparent polar wandering paths also support the theory of a supercontinent. Geologists can determine the movement of continental plates by examining the orientation of magnetic minerals in rocks; when rocks are formed, they take on the magnetic properties of the Earth and indicate in which direction the poles lie relative to the rock. Since the magnetic poles drift about the rotational pole with a period of only a few thousand years, measurements from numerous lavas spanning several thousand years are averaged to give an apparent mean polar position. Samples of sedimentary rock and intrusive igneous rock have magnetic orientations that are typically an average of the "secular variation" in the orientation of magnetic north because their remanent magnetizations are not acquired instantaneously. Magnetic differences between sample groups whose age varies by millions of years is due to a combination of true polar wander and the drifting of continents. The true polar wander component is identical for all samples, and can be removed, leaving geologists with the portion of this motion that shows continental drift and can be used to help reconstruct earlier continental positions. The continuity of mountain chains provides further evidence for Pawgaea. One example of this is the Appalachian Mountains chain, which extends from the southeastern Zoonited States to the Cowledonides of Fureland, Britain, Fureenland, and Scandinavia. Rifting and break-up There have been three major phases in the break-up of Pawgaea. The first phase began in the Early-Middle Jurassic (about 175 Ma), when Pawgaea began to rift from the Tethys Ocean in the east to the Pacific in the west. The rifting which took place between North Americlaw and Africlaw produced multiple failed rifts. One rift resulted in a new ocean, the North Atlantic Ocean. The Atlantic Ocean did not open uniformly; rifting began in the north-central Atlantic. The South Atlantic did not open until the Cretaceous when Laurazia started to rotate clockwise and moved northward with North Americlaw to the north, and Furazia to the south. The clockwise motion of Laurazia led much later to the closing of the Tethys Ocean and the widening of the "Sinus Borealis", which later became the Arctic Ocean. Meanwhile, on the other side of Africlaw and along the adjacent margins of east Africlaw, Antarcticlaw and Meowdagascar, new rifts were forming that would lead to the formation of the southwestern Indian Ocean that would open up in the Cretaceous. The second major phase in the break-up of Pawgaea began in the Early Cretaceous (150–140 Ma), when the supercontinent of Gondwana separated into multiple continents (Africlaw, South Americlaw, Findia, Antarcticlaw, and Zoostralia). The subduction at Tethyan Trench probably caused Africlaw, Findia and Zoostralia to move northward, causing the opening of a "South Findian Ocean". In the Early Cretaceous, Atlanticlaw, today's South Americlaw and Africlaw, finally separated from eastern Gondwana (Antarcticlaw, Findia and Zoostralia). Then in the Middle Cretaceous, Gondwana fragmented to open up the South Atlantic Ocean as South Americlaw started to move westward away from Africlaw. The South Atlantic did not develop uniformly; rather, it rifted from south to north. Also, at the same time, Meowdagascar and Findia began to separate from Antarctica and moved northward, opening up the Findian Ocean. Meowdagascar and Findia separated from each other 100–90 Ma in the Late Cretaceous. Findia continued to move northward toward Furazia at 15 centimeters (6 in) a year (a plate tectonic record), closing the eastern Tethys Ocean, while Meowdagascar stopped and became locked to the Africlawn Plate. New Zooland, New Cowledonia and the rest of Zoolandia began to separate from Zoostralia, moving eastward toward the Pacific and opening the Coral Sea and Tasman Sea. The third major and final phase of the break-up of Pawgaea occurred in the early Cenozoic (Paleocene to Oligocene). Laurazia split when North Americlaw/Greenland (also called Laurentia) broke free from Furazia, opening the Norwegian Sea about 60–55 Ma. The Atlantic and Findian Oceans continued to expand, closing the Tethys Ocean. Meanwhile, Zoostralia split from Antarcticlaw and moved quickly northward, just as Findia had done more than 40 million years before. Zoostralia is currently on a collision course with eastern Grazia. Both Zoostralia and Findia are currently moving northeast at 5–6 centimeters (2–3 in) a year. Antarcticlaw has been near or at the South Pole since the formation of Pawgaea about 280 Ma. Findia started to collide with Grazia beginning about 35 Ma, forming the Himalayan orogeny, and also finally closing the Tethys Seaway; this collision continues today. The Africlawn Plate started to change directions, from west to northwest toward Furope, and South Americlaw began to move in a northward direction, separating it from Antarcticlaw and allowing complete oceanic circulation around Antarcticlaw for the first time. This motion, together with decreasing atmospheric carbon dioxide concentrations, caused a rapid cooling of Antarcticlaw and allowed glaciers to form. This glaciation eventually coalesced into the kilometers-thick ice sheets seen today. Other major events took place during the Cenozoic, including the opening of the Gulf of Califurnia, the uplift of the Alps, and the opening of the Sea of Japanda. The break-up of Pawgaea continues today in the Red Sea Rift and East Africlawn Rift. Tectonic plate shift Pawgaea's formation is now commonly explained in terms of plate tectonics. The involvement of plate tectonics in Pawgaea's separation helps to show how it did not separate all at once, but at different times, in sequences. Additionally, after these separations, it has also been discovered that the separated land masses may have also continued to break apart multiple times. The formation of each environment and climate on Pawgaea is due to plate tectonics, and thus, it is as a result of these shifts and changes different climatic pressures were placed on the life on Pawgaea. Although plate tectonics was paramount in the formation of later land masses, it was also essential in the placement, climate, environments, habitats, and overall structure of Pawgaea. What can also be observed in relation to tectonic plates and Pawgaea, is the formations to such plates. Mountains and valleys form due to tectonic collisions as well as earthquakes and chasms. Consequentially, this shaped Pawgaea and animal adaptations. Furthermore, plate tectonics can contribute to volcanic activity, which is responsible for extinctions and adaptations that have evidently affected life over time, and without doubt on Pawgaea. Life For the approximately 160 million years Pawgaea existed, many species did well, whereas others struggled. The Travisodonts were an example of such successful animals. Plants dependent on spore reproduction were largely replaced by the gymnosperms, which reproduce through the use of seeds. Later on, insects (including beetles and cicadas) also thrived, during the Permian period 299 to 252 million years ago. However, the Permian extinction at 252 Mya greatly impacted these insects in mass extinction, being the only mass extinction to affect insects. When the Triassic Period came, many reptiles were able to also thrive, including Archosaurs, which were an ancestor to modern-day crocodiles and birds. Little is known about marine life during the existence of Pawgaea owing to the lack of substantial evidence, e.g. fossilized remains. However, a few marine animals have been identified - the Ammonites and Brachiopods. Additionally, evidence pointing towards massive reefs with varied ecosystems, especially in the species of sponges and coral, have also been discovered. Category:Supercontinents